TableDef.ValidationRule Property (DAO)
Sets or returns a value that validates the data in a field as it's changed or added to a table (Microsoft Access workspaces only).Read/write String.
The settings or return values is a String that describes a comparison in the form of an SQL WHERE clause without the WHERE reserved word. For an object not yet appended to the Fields collection, this property is read/write.
The ValidationRule property determines whether or not a field contains valid data. If the data is not valid, a trappable run-time error occurs. The returned error message is the text of the ValidationText property, if specified, or the text of the expression specified by ValidationRule.
Validation is supported only for databases that use the Microsoft Access database engine.
The string expression specified by the ValidationRule property of a Field object can refer only to that Field. The expression can't refer to user-defined functions, SQL aggregate functions, or queries. To set a Field object's ValidationRule property when its ValidateOnSet property setting is True, the expression must successfully parse (with the field name as an implied operand) and evaluate to True. If its ValidateOnSet property setting is False, the ValidationRule property setting is ignored.
The ValidationRule property of a Recordset or TableDef object can refer to multiple fields in that object. The restrictions noted earlier in this topic for the Field object apply.
For a TableDef object based on an linked table, the ValidationRule property inherits the ValidationRule property setting of the underlying base table. If the underlying base table doesn't support validation, the value of this property is a zero-length string ("").
If you set the property to a string concatenated with a non-integer value, and the system parameters specify a non-U.S. decimal character such as a comma (for example, strRule = "PRICE > " & lngPrice, and lngPrice = 125,50), an error will result when your code attempts to validate any data. This is because during concatenation, the number will be converted to a string using your system's default decimal character, and Microsoft Access SQL only accepts U.S. decimal characters.